Thermoplastic moulding materials based on acrylonitrile, styrene and butadiene

1. A graft copolymer B constructed from:

B1: 40 to 85 wt %, based on the solids content of the graft copolymer B, of a graft substrate (B1) obtained by (a) polymerizing:

(B11): 10.5 to 24.5 wt %, based on the graft substrate B1, of at least one vinylaromatic, and

(B12): 75.5 to 89.5 wt %, based on the graft substrate B1, of at least one diene,

where (B11) and (B12) sum to 100 wt %;

and (b) agglomerating the obtained graft substrate B1 by adding

(C): 0.01 to 5 parts by weight, based on 100 parts by weight of the graft substrate B1, in each case based on the solids content, of an agglomerating copolymer (C) of:

(C1): 80 to 99.9 wt % of one or more C 1 to C 12 alkyl acrylates or C 1 to C 12 alkyl methacrylates and

(C2): 0.1 to 20 wt % of one or more comonomers selected from the group consisting of acrylamide and methacrylamide,

where (C1) and (C2) sum to 100 wt %; and

B2: 15 to 60 wt %, based on the solids content of the graft copolymer B, of a graft sheath obtained by reacting the agglomerated graft substrate B1 with a mixture of:

(B21) 70 to 90 wt %, based on the graft sheath (B2), of styrene and/or α-methylstyrene, and

(B22) 10 to 30 wt %, based on the graft sheath (B2), of acrylonitrile and/or methyl methacrylate,

where the graft substrate B1 and the graft sheath B2 sum to 100 wt % in total; and where

(i) the agglomerating copolymer (C) has a polydispersity U in the range of from 0.26 to 0.20 and a d 50 value in the range of from 110 to 140 nm; and

(ii) the agglomerated graft substrate B1 has a bimodal particle size distribution of a fraction x) of nonagglomerated particles having a d 50 value in the range of from 80 to 120 nm and a fraction y) of agglomerated particles having a d 50 value in the range of from 350 to 450 nm and a polydispersity U in the range of from 0.27 to 0.20.

2. The graft copolymer according to claim 1 , characterized in that the copolymer (C) is a copolymer of 92 to 98 wt %, based on the total solids in (C), of ethyl acrylate and 2 to 8 wt %, based on the total solids in (C), of methacrylamide having a polydispersity U in the range of from 0.26 to 0.20 and a d 50 value in the range of from 110 to 140 nm.

3. The graft copolymer according to claim 1 , characterized in that the graft copolymer is constructed from:

B1: 40 to 85 wt %, based on the solids content of the graft copolymer B, of a graft substrate (B1) obtained by (a) polymerizing:

(B11): 10.5 to 24.5 wt %, based on the graft substrate B1, of styrene, and

(B12): 75.5 to 89.5 wt %, based on the graft substrate B1, of butadiene,

where (B11) and (B12) sum to 100 wt %;

and (b) agglomerating the obtained graft substrate B1 by adding

(C): 0.01 to 5 parts by weight, based on 100 parts by weight of the graft substrate B1, in each case based on the solids content, of an agglomerating copolymer (C) of:

(C1): 80 to 99.9 wt % of ethyl acrylate and

(C2): 0.1 to 20 wt % of methacrylamide,

where (C1) and (C2) sum to 100 wt %; and

B2: 15 to 60 wt %, based on the solids content of the graft copolymer B, of a graft sheath obtained by reacting the agglomerated graft substrate B1 with a mixture of:

(B21) 70 to 90 wt %, based on the graft sheath B2, of styrene, and

(B22) 10 to 30 wt %, based on the graft sheath B2, of acrylonitrile,

where the graft substrate B1 and the graft sheath B2 sum to 100 wt % in total; characterized in that

(i) the agglomerating copolymer (C) has a polydispersity U in the range of from 0.26 to 0.20 and a d 50 value in the range of from 110 to 140 nm, and

(ii) the agglomerated graft substrate B1 has a bimodal particle size distribution of a fraction x) of nonagglomerated particles having a d 50 value in the range of from 80 to 120 nm and a fraction y) of agglomerated particles having a d 50 value in the range of from 350 to 450 nm and a polydispersity U in the range of from 0.27 to 0.20.

4. The graft copolymer according to claim 1 , characterized in that the copolymer (C) is a copolymer of 92 to 98 wt % of ethyl acrylate and 2 to 8 wt % of methacrylamide having a polydispersity U in the range of from 0.25 to 0.21 and a d 150 value in the range of from 115 to 140 nm.

5. A process for producing a graft copolymer B according to claim 1 by:

(i) polymerizing the monomers B12 and B11 in aqueous emulsion to afford a particulate graft substrate B1,

(ii) agglomerating the particulate graft substrate B1 which is in the form of an emulsion using an agglomerating copolymer (C), wherein the copolymer (C) has a polydispersity U in the range of from 0.26 to 0.20 and a d 50 value in the range of from 110 to 140 nm to afford an agglomerated particulate graft substrate B1, and subsequently

(iii) polymerizing the monomers B21 and B22 of the graft sheath in aqueous emulsion in the presence of the agglomerated particulate graft substrate B1.

6. The process according to claim 5 , wherein step (i) is characterized by:

(i) polymerizing the monomers B12 and B11 in aqueous emulsion to afford a particulate graft substrate B1, wherein

(i-I) initially only monomer (B11) is polymerized in an amount of from 3 to 10 wt %, based on the total monomer amount (B11) and (B12), and

(i-II) subsequently a mixture of monomer (B12) and the remaining monomer (B11) is polymerized.

7. A thermoplastic molding compound comprising

a thermoplastic copolymer A and a graft copolymer B according to claim 1 and optionally further components K, wherein the molding compound comprises:

A: 40 to 80 wt % of at least one thermoplastic copolymer A obtained from:

A1: 20 to 31 wt %, based on the copolymer A, of acrylonitrile and

A2: 69 to 80 wt %, based on the copolymer A, of styrene or α-methylstyrene or a mixture of styrene and α-methylstyrene,

B: 20 to 60 wt % of the graft copolymer B;

and

K: 0 to 5 wt % of further components K,

where the components A, B, and K sum to 100 wt %.

8. The thermoplastic molding compound according to claim 7 , characterized in that the copolymer A is constructed from the monomers styrene and acrylonitrile.

9. The thermoplastic molding compound according to claim 7 , characterized in that said compound additionally comprises at least one further thermoplastic polymer (TP) selected from the group consisting of polycarbonates, polyester carbonates, polyesters, and polyamides.

10. A method of processing a thermoplastic molding compound according to claim 7 for producing molded articles.

11. A process for producing a copolymer (C) comprising a core constructed from at least one of the monomers cited as component (C1), wherein this core is grafted with a copolymer constructed from the components (C1) and (C2) by an emulsion polymerization comprising the steps of:

(x) emulsion polymerizing at least one monomer (C1) in a first step, and

(y) adding a monomer mixture comprising monomers (C1+C2) in a further step,

characterized in that the steps (x) and (y) are performed in the presence of at least one emulsifier which is employed in an amount of from 0.05 to 0.50 wt % in step (x),

and in an amount of from 0.45 to 4.50 wt % in step (y), in each case based on the total monomer content of the copolymer (C) in the entire process;

wherein (C) is an agglomerating copolymer of:

(C1): 80 to 99.9 wt % of one or more C 1 to C 12 alkyl acrylates or C 1 to C 12 alkyl methacrylates and

(C2): 0.1 to 20 wt % of one or more comonomers selected from the group consisting of acrylamide, and methacrylamide,

where (C1) and (C2) sum to 100 wt %; and

wherein the agglomerating copolymer (C) has a polydispersity U in the range of from 0.26 to 0.20 and a d50 value in the range of from 110 to 140 nm.

12. A copolymer (C) obtained by the process according to claim 11 .